1. Field of the Invention
The invention relates to a water-based latex of an acrylic modified waterborne alkyd dispersion in water. Such acrylic modified waterborne alkyds are useful in a variety of coating compositions.
2. Description of Related Art
In recent years, considerable effort has been expended by the coatings industry to develop low or zero VOC containing coating formulations. Regulations to limit the amount of VOC content of industrial coatings have encouraged research and development to explore new technologies directed at reducing solvent emissions from industrial solvent-based coatings operations such as automotive, appliance, general metal, furniture, and the like. One technology involves the replacement of organic solvents with water and is of particular interest for the obvious reasons of availability, cost, and environmental acceptability. However, while the move from organic solvent-based compositions to aqueous compositions brings health and safety benefits, aqueous coating compositions must meet or exceed the performance standards expected from solvent-based compositions. The need to meet or exceed such performance standards places a premium on the characteristics and properties of waterborne polymer dispersions used in aqueous coating compositions.
Waterborne polymer dispersions have been prepared from each of the three primary industrial film-forming polymer types: polyesters, acrylics and alkyds. Of the three polymer types, waterborne alkyd resins exhibit significantly higher storage stability and coating stability than the waterborne polyester or acrylic resins. In addition, alkyd resins, due to their low molecular weight, exhibit exceptional film forming ability which translates into very high gloss in the final coating film. Resistance properties are developed, as with traditional solvent-borne alkyds, via autooxidative crosslinking of the alkyd film. However, while alkyd polymers have shown, and continue to show promise, they have relatively slow "dry" and/or cure times, particularly at ambient temperatures. In an attempt to address such concerns, hybrids of waterborne alkyds and relatively high molecular weight acrylic polymers have received considerable attention.
U.S. Pat. No. 4,413,073 describes the preparation of an aqueous dispersion of particles of a film-forming polymer comprising a pre-formed polymer and at least one polymer formed in situ ("multi-polymer particles"). The dispersion is prepared in the presence of an amphipathic stabilizing compound having an HLB of at least 8 and whose lipophilic portion comprises at least one ethylenic unsaturation. The aqueous dispersion is useful as a film-forming component of coating compositions.
U.S. Pat. No. 4,451,596 describes water-dilutable alkyd and acrylate resins for use in water-dilutable lacquer systems. A method for the preparation of water-dilutable resin preparations based upon alkyd and acrylate resins is also described.
European Patent Application 0 555 903 describes a water-dispersible hybrid polymer of an unsaturated fatty acid-functionalized polyester. In addition, aqueous dispersions of such a hybrid polymer for use in aqueous coating compositions with a high solids content and films produced by using such coating compositions are described.
PCT Application WO 95/02019 describes an emulsion of an air-drying resin dispersed in water and the preparation of such emulsions. Hybrid emulsions of an alkyd resin and an acrylate resin are also described.
Previous alkyd/acrylic hybrid latexes have been prepared using alkyds which do not contain metal sulfonate groups. Further, the acrylic polymers of these previous hybrids are either non-reactive or possess reactive groups (e.g. hydroxyl groups) which react, as do similar groups present in the alkyd resin, with aminoplasts such as melamine formaldehyde resins and only at elevated temperatures.